The argument might be easier to understand if we can find other examples of "signaling hazard" dynamics. For example, well-read people in the current year are often aware of various facts that they're careful never to acknowledge in public for fear of being seen as right-wing (racist, sexist, homophobic, transphobic, _&c._). In this context, the analogous dismissal, "Why do you care if someone isn't sure you're progressive? What's wrong with being right-wing?", doesn't seem compelling. _Of course_, we care; _of course_, there's something wrong with it.
The argument might be easier to understand if we can find other examples of "signaling hazard" dynamics. For example, well-read people in the current year are often aware of various facts that they're careful never to acknowledge in public for fear of being seen as right-wing (racist, sexist, homophobic, transphobic, _&c._). In this context, the analogous dismissal, "Why do you care if someone isn't sure you're progressive? What's wrong with being right-wing?", doesn't seem compelling. _Of course_, we care; _of course_, there's something wrong with it.